Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $106.54   11.815%   $119.1277   $119.13   $119.15   $119.10  
  Purchase #2 $211.82   6.509%   $225.6074   $225.61   $225.60   $225.60  
  Purchase #3 $126.59   7.372%   $135.9222   $135.92   $135.90   $135.90  
  Purchase #4 $142.39   9.123%   $155.3802   $155.38   $155.40   $155.40  
  Purchase #5 $74.31   9.497%   $81.3672   $81.37   $81.35   $81.40  
  Purchase #6 $230.95   11.779%   $258.1536   $258.15   $258.15   $258.20  
  Purchase #7 $46.61   12.372%   $52.3766   $52.38   $52.40   $52.40  
  7 purchase totals = $939.21       $1,027.9349   $1,027.94   $1,027.95   $1,028.00